每隔几秒自动刷新或更新内容页面 [英] Refresh or update content page every few seconds automatically

问题描述

我正在使用 Xamarin.forms (PCL)，我需要每隔几秒刷新/更新内容页面的数据.从 viewmodel 中的 API 检索数据.

I am using Xamarin.forms (PCL) and I need to refresh/update Content Page with its data every few seconds. The data is retrieved from API in the viewmodel.

是否有任何方法或处理程序可以定期用于在 page.xaml.cs 中定期调用 Get Api，例如:

Is there any method or handler that can be used periodically to call the Get Api periodically inside the page.xaml.cs, something like:

methodRunPeriodically()
{
 userdata = await UserService.GetUserasync(_UserViewModel.EmployeeId);
}

推荐答案

基于上述问题中的代码，您将确保:

Based on the code in the above question, you would ensure that:

1. 您的 userdata 对象实现 IPropertyChange 如下:

1. Your userdata object implements IPropertyChange as follows:

//Other usings skipped for brevity
...
...
using System.ComponentModel;
using System.Runtime.CompilerServices;

// This is a simple user class that 
// implements the IPropertyChange interface.
public class DemoUser : INotifyPropertyChanged
{
    // These fields hold the values for the public properties.
    private string userName = string.Empty;
    private string phoneNumber = string.Empty;

    public event PropertyChangedEventHandler PropertyChanged;

    // This method is called by the Set accessor of each property.
    // The CallerMemberName attribute that is applied to the optional propertyName
    // parameter causes the property name of the caller to be substituted as an argument.
    private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public DemoUser()
    {
    }
    public string Id { get; set; }
    public string UserName
    {
        get
        {
            return this.userName;
        }

        set
        {
            if (value != this.userName)
            {
                this.userName = value;
                NotifyPropertyChanged();
            }
        }
    }

    public string PhoneNumber
    {
        get
        {
            return this.phoneNumber;
        }

        set
        {
            if (value != this.phoneNumber)
            {
                this.phoneNumber = value;
                NotifyPropertyChanged();
            }
        }
    }
}

然后在您的 ContentPage 中尝试以下操作(我对上面其他人的代码稍作修改):

In your ContentPage, you then try the following, (I slightly modified the code by others above):

public class UserPage : ContentPage
{
    private DemoUser demoUser;
    private int intervalInSeconds;

    public UserPage()
    {
        //Assuming this is a XAML Page....
        InitializeComponent();
    }
    public UserPage(DemoUser demoUser, int intervalInSeconds = 10) : this()
    {
        this.demoUser = demoUser;
        this.intervalInSeconds = intervalInSeconds;

        this.BindingContext = this.demoUser; 

        Device.StartTimer(TimeSpan.FromSeconds(this.intervalInSeconds), () =>
        {
            Device.BeginInvokeOnMainThread(() => refreshDemoUser());
            return true;
        });
    }

    private async void refreshDemoUser()
    {
        this.demoUser = await getDemoUserById(this.demoUser.Id);
    }
}

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